When you want to see the stars, find someplace dark
A bad indicator LED, a simple ten cent part brought the Keck 1 telescope to a stop this last week.
I was getting ready to leave the summit when the radio started to speak words of concern, it sounded like something was not working, an instrument rotator?
Worse, the Keck 1 computer room hosted a veritable crowd, from the summit supervisor to all of the techs. Yeah, this was not good, why are they all looking at me? Oh, h%#*!
The golden yellow glow that has dominated the night for generations is disappearing.
The yellow glow of sodium light has been both celebrated and reviled. While the glow can be attractive in night scenery it also creates inhuman tones in faces and photos of people. Movies have been shot under sodium lights, songs reference the golden glow. Astronomers both professional and amateur prefer the lights as the light can be easily filtered from view.
It may be the day after Thansgiving, but that did not stop the electrical contractors installing new streetlamps in Waikoloa Village.
We are not sad to see the old low pressure sodium light go, it has been a nuisance. The poorly designed sodium lamp creating glare into our windows We had called to complain with the county, but nothing was ever done. The glare intruded on our bedroom window, a real issue, somewhat alleviated by the growth of our plumeria along the front blocking the light, a deliberate solution on my part.
The big question is whether the new LED light improves the astronomy situation from my driveway. The old sodium lamps along the street made it impossible to do visual observing, there was simply too much glare. The new lamps should darken the sky and create far less light directed at my driveway.
Even better, the lamps in question are C&W Energy Star Friendly® units with reduced blue emissions. Elimination of almost all of the blue light greatly reduces scatter in the atmosphere and is better for the observatories.
With the old light I was able to do astrophotography from the driveway using an LPR filter that blocked the 589nm of sodium light. The new lights will have a broader spectrum and be more difficult to block. On the other hand they send very little light upwards, possibly improving the situation. It will be interesting to see what the difference is. When the Moon is a few days further gone I will have to setup the camera and find out.
It may also be a good idea to check the old CloudCam images against new images as the replacement continues. It will be interesting to see if the emissions from the neighborhood are effectively reduced as seen from the top of the mountain.
The changeover is inevitable. LEDs are the most power-efficient commercially available light source. Their longer lifetimes, greater light-per-watt and lower installation costs make it only a matter of time before most light sources in the world are LED. The fixtures and bulbs are still notably more expensive, but that’s offset by lower energy usage and longer lifetimes.
Streetlights consume an enormous amount of the power generated across the globe. Here in the islands, where power is more expensive than much of the nation, the power savings make LED streetlights very attractive. As Hawai’i County taxpayers this is something that we should all be concerned with, we pay the power bill for the thousands of streetlights across the island.
The best competing technology is low pressure sodium (LPS). It is this streetlight technology that is currently used throughout Hawai’i. LPS emits all of its light at a single wavelength, 589nm, a golden yellow. Many people dislike the yellow color, and it can be confused with the yellow of a changing intersection signal. The large LPS bulbs are difficult to design fixtures around, resulting in lamps that throw light in all directions, not just where needed. As a result, many LPS fixtures create a lot of glare for drivers and surrounding homes and businesses.
LPS lights do have advantages, of course. They are quite power efficient, emitting all the light near the peak sensitivity of the human eye. Astronomers prefer the light of LPS lamps, as the single wavelength can be easily filtered or simply ignored when seen in their data. Between the power savings and the astronomy friendly aspects, LPS had been the outdoor lighting of choice across the state. The result is the familiar golden glow above any urban area in the islands.
But change is coming, with LEDs already beginning to replace LPS streetlights. Hawai’i County has planned for some time to convert to LED technology and evaluation of the new lamps has been going on at several test locations. With the success of those tests more widespread deployment is just beginning. This last month the new LED streetlights were installed around the town of Waimea. For many this is the first chance to see the new lights in place.
The recent conversion allowed an opportunity to compare the new with the old. Taken midway through the change out, the photo shows the new lights down the right side of the street, while the older low pressure sodium lights have yet to be replaced on the left side of the street. In order to faithfully reproduce the scene, the photo was taken in raw mode with daylight white balance used to produce the image shown.
The new lights are dramatically better than the old, unshielded LPS lights. Because of their vastly reduced glare, you simply do not see the lights themselves from any distance. Even nearby the lights do not produce the distracting glare of the older designs. Note, also, that all of the older LPS lights create yellow halos of glare in the photo, all the way down the street. While the new LED lights become hard to see once you are out from underneath the light. In the photo, the third LED light from the camera is just seen and the fourth is hard to pick out.
The improvement is immediately noticeable while driving the main street of Waimea. The LED lights are difficult to see directly, while the light provided on the roadway is just as good if not better than the older LPS fixtures. This is a street that has substantial pedestrian traffic and other vehicles pulling in and out of the many businesses, so good visibility is critical for safety.
The comparison here is not completely fair. The low pressure sodium fixtures used on much of the island, including Waimea are poor examples of modern lighting design. Well-designed low pressure sodium fixtures would compare somewhat more favorably. Still, LED’s are easier light sources to design a decent fixture around because LED’s are nearly point sources, not a large gas tube. Designing a good reflector and a decent cutoff shield is quite difficult for low pressure sodium bulbs.
One advantage of the better light design is reduced “light trespass.” That means less light shining onto areas where it is not needed. Directing the light properly onto the roadway means less light shining into the windows of adjacent homes, or upwards to light the sky and outwards to confuse birds or sea turtles.
Additionally, the new LED lamps installed on the island have specially designed blue cutoff filters. This is critical for the observatories. White LED lights use a blue or violet LED to excite a phosphor that converts the blue light to a white light. After the conversion a large amount of this blue light leaks through the phosphor. It is this blue light that is most troubling to astronomers because it readily scatters in air, an effect called Rayleigh scattering. This is the same effect that makes the sky blue during the day. The sky is naturally darker in the blue region of the spectrum, thus any light pollution at this wavelength creates a larger impact on astronomy. The special filters, therefore, keep the LED lamps from backfiring and creating more light pollution.
So far Hawai’i County’s conversion to LED lights is just beginning. One thousand lamps were ordered, and only a handful have been installed so far, mostly near intersections. While we hope that the effects improve safety, reduced light pollution, and reduced power bills, it will be some time before we see the real impact of the new lights and have a chance to measure the changes.
Need a red lamp to provide soft red illumination around the telescope? Described here is an easy way to do this. Take a commonly available desklamp and convert it to LED’s. This is a single evening project, taking just a few hours to accomplish once the parts have been obtained.
I have found the resulting light extremely useful when observing. No more holding the flashlight in your mouth when reading charts or making observing notes.
Because the light can light up a whole area when turned fully on it can be used as a worklight when breaking down gear and packing it into the vehicle without bothering other observers at a dark observing site. Or you might build the 120V version for a personal observatory.
I have also found that these lights also make great gifts for fellow astronomers.
To accomplish this we will disassemble the lamp, remove the 12V bulb and replace it with an array of LED’s. To control the brightness we will install a variable regulator to allow dimming of the lamp from completely off to very bright. An option is to install another connector to allow DC power to be supplied from a battery for field use.
Before embarking on this project be sure to read this entire article. Having the entire task in mind will help you plan ahead. It is important to use safe electronic assembly techniques to avoid any risk of damage or injury when making the modifications or when using the lamp. We will make no modifications to the high voltage side of the transformer to insure the lamp remains safe to use.
One secret to the lamp is the LED’s. These wonderful devices convert a small trickle of electricity into a very bright red light. Be sure to get ‘Ultrabright’ or ‘Superbright’ types that put out at least 3000mCd (millicandela). I found some that put out 6000mCd that I use in my lights at All Electronics. Perfboard, regulators and many of the other parts can also be purchased there.
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